Alcohols fill an important role in industry. They are often used as intermediates for the preparation of lubricant oils, fats, plasticizers, pharmaceuticals, cosmetics and flavourings. Alcohols are also used directly as solvents, antifreeze agents or fuel additives.
Plasticizers are used in large amounts for modifying the thermoplastic properties of numerous industrially important products such as plastics for example, but also paints, coating compositions, sealants etc. An important class of plasticizers are the ester plasticizers which include, inter alia, phthalic esters, trimellitic esters, phosphoric esters etc. The alcohols used for producing ester plasticizers are generally referred to as plasticizer alcohols. To produce ester plasticizers having good performance properties, there is a need for plasticizer alcohols having about 5 to 12 carbon atoms.
Due to the phthalate discussion in the plasticizer sector, the demand for novel phthalate-free plasticizers is increasing. It is critical in this case, however, that the respective plasticizers must meet narrow specifications with regard to their properties with respect to the applications. Examples here include the viscosity or the volatility of the plasticizers. Control of the essential properties of the plasticizers depends in this case less on the esterification reaction typically used in the production of plasticizers but rather on the raw materials used, especially the alcohols used. Essential factors here are, for example, the number of carbon atoms of the alcohols used or the isomer distribution thereof. For this purpose, alcohols having 4, 5 or 6 carbon atoms for example are suitable. At the same time, however, it is also necessary to produce the C8-, C10- and C12-alcohols described.
One of the best-known routes to alcohols is the hydroformylation reaction in which alkenes are converted to aldehydes, which are then subjected to a hydrogenation, in order to produce the corresponding alcohols (Cn-alcohols). An exception here is the hydroformylation of propene and unbranched butenes. Here, the resulting aldehydes are usually subjected to a further reaction step, the aldolization, in order to produce long-chain unsaturated aldehydes. These are then also subjected to a hydrogenation and the longer-chain alcohols (C2n-alcohols) obtained are used for the most part in the production of phthalate-containing plasticizers.
For instance, EP 1004563 describes the preparation of alcohols by hydroformylation of an olefin, aldol condensation of a portion of the aldehyde and subsequent hydrogenation reaction. However, specific control of the composition of the alcohols obtained is not possible in this manner.
The challenge that arises therefrom is on the one hand to control the isomer distribution of the alcohols to be produced, and on the other hand however also to control especially the ratio of Cn- to C2n-alcohols.